Ion implantation is utilized in the fabrication of semiconductor based devices such as Light Emitting Diodes (LED), solar cells, and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). Ion implantation is used to introduce dopants to alter the electronic or physical properties of semiconductors.
In a traditional ion implantation system, a gaseous species often referred to as the dopant source is introduced in to the arc chamber of an ion source. The ion source chamber comprises a cathode which is heated to its thermionic generation temperature to generate electrons. Electrons accelerate towards the arc chamber wall and collide with the dopant source gas molecule present in the arc chamber to generate a plasma. The plasma comprises dissociated ions, radicals, and neutral atoms and molecules of the dopant gas species. The ions are extracted from the arc chamber and then separated to pick a desired ionic species which is then directed towards the target substrate.
Tin (Sn) is recognized as a dopant with many uses. For example, tin (Sn) has emerged as a suitable dopant in germanium (Ge) to create strain in Ge and improve the flow of electrons and holes through Ge in a transistor. Additionally, Sn has also been explored as an active dopant species for III-V semiconductor devices.
Sn has been used in semiconductor devices. Sn can function in various ways, including as a gate oxide and gate electrode metal in metal-oxide-semiconductor field-effect transistors (MOSFETs); a dopant in copper (Cu) interconnects to prevent electro migration; and as an intrinsic getter in silicon (Si). Sn is generally deposited on a substrate using Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD). In PVD, Sn metal is heated in vacuum using an electron beam to heat a crucible of Sn or a Sn-containing compound. As the crucible temperature increases, the vapor pressure of Sn in the crucible increases and Sn vapor deposits on a substrate. CVD is a similar technique except the dopant source is a volatile Sn compound and will react with the substrate when deposited therein.
For example, mixtures of Sn(CH3)4 with either CF3I or CF3Br compounds can be co-deposited with O2 at elevated temperatures on a heated substrate to produce films of SnO2. Sn can also be embedded in the surface of a substrate using ion implantation. In one method of ion implantation, Sn metal is placed in close proximity to a filament and the temperature of the filament is high enough that radiative heating causes Sn to evaporate and collide with electrons to create Sn ions for doping. However, this method can cause Sn to deposit on the chamber walls or on the filament, shortening the filament lifetime.
There is no currently viable Sn dopant source available today for ion implantation. For these reasons, there is an unmet need for a Sn dopant source that can be used in traditional ion implantation systems.